The present invention relates to a machined retainer of rolling bearing.
A machined retainer of rolling bearing is a retainer made by machining/grinding forged products, bar materials or cast ones, and ordinarily it is formed with Cu alloys. In particular, high strength brass materials where brass is added with Al, Mn, Ni and Fe are of self-lubricity and suited as materials for retainers requiring abrasion resistance, seizure resistance and mechanical strength. As the high strength brass materials for machined retainers conventionally employed, the high strength brass cast-Category 1 (HBsC1) by JIS or the high strength brass cast-Category 2 (HBsC2) may be taken up.
On the other hand, as the using conditions of rolling bearings have recently been severe, retainers have also been demanded to possess high processing precision. Especially, if a column of the retainer is tilted, the column and the rolling body interfere each other and issue creaking, so that sound effect is deteriorated. Therefore, in recent times, a free-cutting brass which is higher in the machinability than the high strength brass has been used as the Cu alloy for the machined retainer.
The free-cutting brass (for example, Brass cast-Category 3: YBsC3) is a material where Pb is added to brass. In the free-cutting brass material, a high cutting property can be provided in that Pb grains scattered in a base material serve as a chip breaker reducing a cutting stress.
However, since the free-cutting brass is weak in a binding strength between the base material and the Pb grains, the Pb grain is easy to fall off during machining, and traces of this falling-off easily remain in the surface of the retainer after grinding. As a result, there is a risk that coarseness grows larger in the retainer surface and lowers the sound effect.
If the coarseness in the retainer surface is large, amounts of initial abrasion in a pocket face and a guiding face may be large. In such a case, dimensions of the retainer are changed during working, otherwise abrasion powders are mixed as foreigners in a lubricant, and delamination will start from the surface of a bearing ring or a rolling body.
Further, as the Pb grain is very soft, yield stress of the free-cutting brass is low, and plastic deformation easily occurs if excessive stress is loaded during cutting process. Therefore, if the machined retainer is formed with the free-cutting brass, the column of the retainer is plastic-deformed and the sound effect may be deteriorated.
In addition, Pb is a harmful substance to human living bodies and environments, and much Pb addition to brass for heightening the machinability is not desirable also in view of the protection of environment.
Besides, the retainer made with Cu alloy containing much Pb has a room to be improved in the abrasion resistance.
The invention has been established by paying attentions to problems involved with the prior art, and it is a subject matter of the invention to form the machined retainer with such a material having the high machinability, mechanical strength, sound effect and abrasion resistance, and having no problem in regards of safety and the protection of environment.
For solving the problems as mentioned above, it is an object of the invention to provide a machined retainer of rolling bearing made of a material wherein crystals of intermetallic compound are finely dispersed in a base material comprising a Cu alloy.
In the retainer according to the present invention, it is advantageous that the Cu alloy contains Pb 0.4 wt % or lower. In addition, in the retainer according to the present invention, it is preferable that the retainer is formed with the Cu alloy containing Pb 0.1 wt % or lower.
In the retainer according to the present invention, it is also advantageous that the retainer has a surface hardness of which is 110 or higher in Vickers hardness (HV).
Further, in the retainer according to the present invention, it is advantageous that the content percent of the intermetallic compound is 5 to 30% in an area ratio. In addition, it is preferable that the content percent of the intermetallic compound is 8 to 30% in the area ratio.
Furthermore, in the retainer according to the present invention, it is advantageous that at least one element forming the intermetallic compound is selected from the group consisting of Mn, Fe, Si, Co, Ti, Nb, V, Zr, Al and Ni.
Moreover, in the retainer according to the present invention, it is advantageous that the intermetallic compound comprises at least one of Mn5Si3, Cu8Zn2Si and Cu4ZnSi.
Note that in the retainer according to the present invention, the retainer may be made by a centrifugal casting method.
Further, in the retainer according to the present invention, it is advantageous that the Cu alloy is selected from at least one of brass, bronze, phosphorus bronze and aluminum bronze.